The present invention relates to a manually guided implement having an internal combustion engine, especially one embodied as a two-stroke engine.
To achieve a high output and to fulfill the applicable exhaust gas standards, manually guided implements having an internal combustion engine and a carburetor are provided with an appropriate setting of the fuel/air ratio, which is adapted to the hot-running condition of the internal combustion engine. When starting the internal combustion engine after it has been inoperative for a long period of time, and in particular under cold environmental conditions, the mixture provided by the carburetor is too lean and can lead to difficulties in starting the engine.
To improve the starting conditions, especially the cold-start conditions of the internal combustion engine, arrangements are known for enriching the mixture during the starting phase. For example, an increased underpressure can be produced in the intake channel of the carburetor via a starter valve that is disposed in the intake channel ahead of the butterfly valve. Due to the increased underpressure, an increased quantity of fuel is drawn in relative to the quantity of air that is drawn in by the internal combustion engine. The mixture becomes richer, thereby improving the starting conditions. However, a drawback of this arrangement is the increased cost of construction, especially with regard to the kinematic control of the starter valve.
It is also known, for enriching the fuel/air mixture, to provide a so-called primer pump, via which, prior to the start or during the starting process, a predetermined quantity of fuel can be injected into the intake line of the internal combustion engine via a primer line. As a result, a sufficient quantity of fuel is already available during the first rotation of the crankshaft during the starting process. To avoid difficulties during the metering of the fuel via a primer pump, embodiments are known according to which the pump is integrated into the carburetor. By means of a pressure line that is connected with the crankcase of the internal combustion engine, the primer pump is shut off when the internal combustion engine starts. Such a carburetor arrangement has a complex construction and is difficult to adjust with regard to the quantity of fuel that is to be injected.
It is therefore an object of the present invention to improve the starting characteristics of the internal combustion engine of a manually guided implement.